Conventional electron beam lithography machines include machines of a point beam type, which use a spot-shaped beam and machines of a variable rectangular beam type, which use a beam having a rectangular section with a variable size.
An electron beam lithography machine of a point beam type performs drawing by using a single electron beam. Hence, this machine has a low throughput and is used only for research and development. The throughput of an electron beam lithography machine of a variable rectangular beam type is higher than that of a point beam type by one or two orders of magnitude. However, this type also basically executes drawing by using a single electron beam, so there is still a problem of throughput in exposing a pattern in which fine patterns of about 01. μm are integrated at a high density.
As a machine to solve this problem, there is an electron beam lithography machine of a stencil mask type. In this machine, a pattern to be drawn is formed as pattern conduction pores in a stencil mask. Then, the pattern to be drawn is transferred to the sample surface through a reduced electron optical system by irradiating the stencil mask with an electron beam. As another method, a multi-electron beam lithography machine is used. A substrate having a plurality of apertures is irradiated with an electron beam to irradiate a sample surface with a plurality of electron beams from the plurality of apertures through a reduced electron optical system. The sample surface is scanned by deflecting the plurality of electron beams. The plurality of electron beams are individually turned on/off in accordance with the pattern to be drawn, thereby drawing the pattern. In all methods described above, the throughput can be improved because the area to be exposed at once, i.e., the exposure area, is wider than a conventional one.
The reduced electron optical system of an electron beam lithography machine of a stencil mask type or a multi-electron beam lithography machine must be adjusted to suppress aberration in balance in the entire exposure field wider than usual. To do this, it is necessary to separately measure spherical aberration, coma, astigmatism, displacement, and focus position at each image height in the entire exposure field and execute adjustment on the basis of the measurement result. However, in conventional aberration measurement, defocus of a beam and its position are only measured so aberration cannot be suppressed in balance in the entire exposure field.
Japanese Patent Laid-Open No. 2004-153245 (patent reference 1) proposes an astigmatism correction sensitivity deciding method in a charged particle beam lithography machine and an exposure method using the method.